An air conditioning or refrigeration plant can be shut down in response to the sensing of any one of a number of abnormal conditions. While the sensed abnormal condition causing shutdown may be precipitous, it is ordinarily developed over a period of time during which the system condition is in the abnormal range but has not reached a level requiring the system to shut down. It is, therefore, a general practice in some installations, as aboard ship, to monitor the gages, sensors, etc. on a round-the-clock basis. When the system is automatically shut down, the sensed abnormal condition is often removed or is subject to dissipation as in the case of a temperature condition. If the gages and sensors have not been monitored closely or if the condition is precipitous, the condition causing the system to shut down may not be readily known. As a result, correcting the problem may first involve determining the problem which, at times, can be a problem itself.